Android编译Native C的helloworld模块

核心提示：# prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/arm-eabi-gcc -nostdlib -Bdynamic -Wl,-T,build/core/armelf.x -Wl,-dynamic-linker,/system/bin/linker -Wl,--gc-se

# prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/arm-eabi-gcc -nostdlib -Bdynamic -Wl,-T,build/core/armelf.x -Wl,-dynamic-linker,/system/bin/linker -Wl,--gc-sections -Wl,-z,nocopyreloc -o out/target/product/generic/obj/EXECUTABLES/helloworld_intermediates/LINKED/helloworld -Lout/target/product/generic/obj/lib -Wl,-rpath-link=out/target/product/generic/obj/lib -lc -lm out/target/product/generic/obj/EXECUTABLES/helloworld_intermediates/hello.o out/target/product/generic/obj/lib/crtbegin_dynamic.o -Wl,--no-undefined ./prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin/../lib/gcc/arm-eabi/4.2.1/interwork/libgcc.a out/target/product/generic/obj/lib/crtend_android.o

这里值得留意的是参数“-Wl,-dynamic-linker,/system/bin/linker”，它指定了Android专用的动态链接器/system/bin/linker，而不是通常所用的ld.so。

生成的可执行程序可用file和readelf命令来查看一下：

# file out/target/product/generic/obj/EXECUTABLES/helloworld_intermediates/LINKED/helloworld

out/target/product/generic/obj/EXECUTABLES/helloworld_intermediates/LINKED/helloworld: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), not stripped

# readelf -d out/target/product/generic/obj/EXECUTABLES/helloworld_intermediates/LINKED/helloworld |grep NEEDED

0x00000001 (NEEDED) Shared library: [libc.so]

0x00000001 (NEEDED) Shared library: [libm.so]

这是ARM格式的动态链接可执行文件，运行时需要libc.so和libm.so。“not stripped”表示它还没被STRIP。嵌入式系统中为节省空间通常将编译完成的可执行文件或动态库进行STRIP，即去掉其中多余的符号表信息。在前面“make helloworld showcommands”命令的最后我们也可以看到，Android编译环境中使用了out/host/linux-x86/bin/soslim工具进行STRIP。

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Android所用的Toolchain(即交叉编译工具链)可从下面的网址下载：

http://android.kernel.org/pub/android-toolchain-20081019.tar.bz2。如果下载了完整的Android项目的源代码，则可以在“/prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin”目录下找到交叉编译工具，比如Android所用的arm-eabi-gcc-4.2.1。